Originally Posted by
B727223Fan
Grebe : and/or improperly checked tooling size ( coldwork mandrel ) is the most likely issue. ( see Fatigue technology )
If the cracks are originating at the fastener holes I do agree with your statement.
Cold Working of holes is very important to relieve stresses as well as proper fastener hole size and proper installation of Hi-Loks.
Hi-Loks are usually installed interference or close tolerance fit.
https://www.aerofastener.com/products/hi-lok-pins
Shot Peening and Flap Peening are also important post assembly maintenance processes on various structural members and parts that also relieves stresses.
Note: I posted this info for folks who have never cold worked holes or installed Hi-Loks.
Thanks - also applies to lock-bolts which use a swaged collar- and at one time early on in 737 program ' taper-loks" may have been used but I'm not sure.
As to cracks and holes - somewhere in this thread are some photos which show exactly that- and early on I had postulated just that kind of problem.
MY guess then and now - is probalby a production change tg ensure coldworking of that area, and a repair of non cracked holes via coldwork and first oversize- awkward to be sure- but cheaper in long run